1. Field of the Invention
The present invention relates to a buck DC-to-DC converter, and more particularly to a buck DC-to-DC converter having a novel output protection mechanism.
2. Description of the Related Art
Please refer to FIG. 1, which illustrates a prior art buck DC-to-DC converter. As illustrated in FIG. 1, the converter includes a buck converter circuit 100, a pair of voltage dividing resistors 160, 170, a first output current sensing resistor 1801, and a second output current sensing resistor 1802, wherein the buck converter circuit 100 includes a controller 110, a switch 120, a diode 130, an inductor 140, and a capacitor 150, and has an input end coupled to a line voltage VLINE, and an output end for providing a DC output voltage VDC.
The controller 110 uses a feedback voltage VFB1 to generate a driving signal VG, and uses feedback voltages VFB2, VFB3, VFB4, and VFB5 to generate a protection signal, wherein the protection signal will disable the driving signal VG to protect the buck converter circuit 100 when the difference between VFB2 and VFB3 exceeds a first predetermined value or the difference between VFB4 and VFB5 exceeds a second predetermined value, that is, when over-current occurs in the first output current sensing resistor 1801, or in the second output current sensing resistor 1802.
The switch 120, the diode 130, the inductor 140, and the capacitor 150 are used to form a buck circuit to convert the line voltage VLINE to the DC output voltage VDC under the control of the controller 110.
The voltage dividing resistors 160, 170 are used to form a voltage divider to divide the DC output voltage VDC, and thereby generate the feedback voltage VFB1.
The first output current sensing resistor 1801 and the second output current sensing resistor 1802 are used to sense a first output current IO1 and a second output current IO2 flowing out the output end of the buck converter circuit 100 respectively, wherein IO1=(VFB2−VFB3)/(the resistance of the resistor 1801), and IO2=(VFB4−VFB5)/(the resistance of the resistor 1802).
When in operation, the feedback voltage VFB1 will be regulated at a reference voltage due to a negative feedback mechanism, and the DC output voltage VDC will thereby be generated; and when IO1 exceeds a first predetermined value—causing the difference between VFB2 and VFB3 larger than a first threshold voltage, or IO2 exceeds a second predetermined value—causing the difference between VFB4 and VFB5 larger than a second threshold voltage, the controller 110 will disable the driving signal VG to stop the power conversion process.
However, as the first output current IO1 and the second output current IO2 are represented by the voltage across the resistors 1801 and the voltage across the resistor 1802 respectively, additional pins have to be added in the controller 100 to attain over-current protection for the prior art buck DC-to-DC converter. Sometimes this can increase the package size of the controller 100 and thereby increase the cost.
In view of the foregoing problem, the present invention proposes a novel buck DC-to-DC converter, which is capable of using less feedback points to attain over-current protection.